The general purpose of this proposal is to analyze some of the complex interactions which exist between neurotransmitter and peptidergic neurons within the hypothalamus. To learn more of how axons from the locus coeruleus (LC) and the medullary Al and A2 regions projects to hypothalamic regions containing LHRH neurons, specific transections and lesions within the hypothalamus will be made. Recent studies show that all LC stimulatory NE axons decussate to reach contralateral LHRH neurons. In these and other studies, anesthetized, estrogen-treated ovariectomized rats will have their medial preoptic nucleus (MPN) electrochemically stimulated (ECS) and, thereafter, the LC, A1 or A2 cell groups will be electrically stimulated (ES). Such LC or A1 ES amplifies LH release. Other studies will examine whether neuroexcitant drugs (e.g. 3-isobutyl-methylxanthine) active NE secretion when microinfused into LC or A1 of unanesthetized rats. The paragigantocellularis nucleus (PGC) in the ventrolateral medulla regulates LC neuronal activity, presumably by releasing excitatory amino acids (EAA). ES of PGC on will be performed to determine if such stimuli increase hypothalamic NE secretion. Other studies will evaluate whether the microinfusion of EAA into LC has a similar excitatory effect in releasing NE and LHRH/LH. Since LHRH neurons may be activated only when specifically coded noradrenergic signals are presented, the parameters of LC or A1 ES will be varied to study how such stimuli affect LHRH neuronal activity. As NE may act via a GABA interneuron, the role of hypothalamic GABA neurons in the regulation of NE-induced LHRH release will be examined. The role of the opiate system in modulating NE secretion also will be studied. In these experiments, specific agonists or antagonists of GABA or opiate receptors will be placed into selective hypothalamic, mid or hindbrain regions and their effects on NE and LHRH secretion following mid or hindbrain ES will be assessed. Changed in NE and LHRH secretion after LC, A1 and A2 ES will be evaluated by HPLC and RIA in dialysates obtained from microdialysis probes placed into specific hypothalamic areas and the pituitary gland. The serotonin (5-HT) system also is to be studied with particular emphasis on how 5-HT and NE interact to excite or inhibit LHRH neuronal activity. Finally, NE and 5-HT interactions with LHRH neurons in androgen-sterilized and male rats are to be examined. These studies should provide important fundamental new information on how the neuroendocrine brain functions to evoke preovulatory gonadotropin surges and ovulation.